Why can't someone steal phone cards?

I was recently in Wal-Mart and these two kids(about 8 or 9) were stealing phone cards, the pre-paid ones, I think tracfone or something like that. The Lady caught them and told them they are worth nothing, so they didn't get in trouble. I didn't think much of it then, but then I started wondering, why wouldn't they work? I mean I took a look at one and you can scratch the foil stuff off and see the number right? So why wouldn't they work? Something about activation? I've been wondering about this. Well, any help is appreciated and won't encourage me to steal, lol. Thanks for any help.

Why can't someone steal phone cards?
They are activated through the POS terminal. They communicate the serial number to the phone company.
Reply:My friend works at Wal-Mart and we usually just have her scan about 10 or 20 200 minute cards for us each week, we never pay though. She just scans them, then we enter the minutes, easy as that.
Reply:They can only be activated at the register... U know kinda like a gift card, but it's for calling people.
Reply:In order for the Cards to work, when they scan it at checkout, it activates the minutes for the activation process when you call in to add them onto your phone.





So you do have to buy them in order for them to actually "be there" .

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